1. Field of the Invention
The present invention relates to an optical correlator system.
Bias level terms, in mathematical equations for optical correlators of known type, degrade the accuracy of the output correlation value because such terms are additive to the true correlation signal. Thus, the correlation values or measurements are degraded by these unwanted bias level terms. Furthermore, such known optical correlators generally have a large dc term in the Fourier transform spectrum due to the unwanted bias terms. This dc term generates a sinc function distribution in the transform spectrum, which results in the side lobe levels of the sinc function being very large in regions of the spectrum, where the signal and reference functions, f(x) and f.sub.R (x), respectively, have significant spectral content. Square law detection also further degrades the measurement.
The principal object of the invention is to provide an optical correlator that uses coherent light which has improved performance.
An object of the invention is to provide an optical correlator which produces no bias error due to recording component characteristics.
An object of the invention is to provide an optical correlator which produces no bias error that is necessarily introduced when bipolar signals and/or reference functions are to be correlated.
Another object of the invention is to provide an optical correlator which utilizes a heterodyne system to eliminate unwanted bias and measurement degradation.
Still another object of the invention is to provide an optical correlator which removes any residual bias error, not accounted for, with a dc blocking aperture in the Fourier transform plane.
Yet another object of the invention is to provide an optical correlator of single structure which functions efficiently, effectively and reliably.
Another object of the invention is to provide an optical correlator which avoids errors due to changing laser frequencies such as mode hops.